We describe the design and implementation of a full-featured Haskell development environment, based on Microsoft’s extensible Visual Studio environment. Visual Haskell provides a number of features not found in existing Haskell development environments: interactive error-checking, displaying of inferred types in the editor, and other features based on static properties of the source code. Visual Haskell also provides full support for developing and building multi-module Haskell projects, based on the Cabal architecture. Visual Haskell supports the full GHC language, and can be used to develop real Haskell applications (including the code of the plugin itself). Visual Haskell has driven developments in other Haskell-related projects: Cabal, the Concurrent FFI extension, and an API to allow programmatic access to GHC itself. Furthermore, development of the Visual Haskell plugin required industrial-strength foreign language interoperability; we describe all our experiences in detail. C...